Electrochemical oxidation of mycophenolate mofetil (MMF) has been studied at a glassy carbon electrode in aqueous solution over a wide pH range. MMF was oxidized on glassy carbon electrode (GCE) by an irreversible process that was controlled mainly by diffusion. The irreversibility of the electrode process was verified by different criteria. A probable mechanism for electrochemical oxidation of MMF was proposed. Differential-pulse voltammogram of the drug showed two oxidation peaks at 0.631 V and at 0.921 V (verses SCE) in phosphate buffer of pH 6.0. This process could be used to determine MMF in the concentration range of5.0×10−7to7.5×10−4 M with a limit of detection of1.48×10−7 M. The method was successfully applied for the analysis of MMF in pure and dosage forms and in biological fluids.

In view of the extensive applications of compounds viz., methdilazine hydrochloride (MDH), promethazine hydrochloride (PMH), and isothipendyl hydrochloride (IPH) as antiallergic drugs, it is necessary to develop new analytical methods for their determination in bulk samples and pharmaceutical preparations. A variety of spectrophotometric methods based on colored complex formation or oxidative reactions have been proposed. Some are lacking sensitivity, 1-6 require heating 7,8 or long standing 9 for color development. The reported methods 1-5 suffer from twin disadvantages of critical acid or oxidant concentration and instability of the colored species, the stability ranging from 10 -40 min. The literature on the extractive spectrophotometric methods for the assay of the above drugs is scanty, although these methods are wellsuited. The official methods [10][11][12] (MDH, 12 PMH, 10 and IPH 11 ) involve non-aqueous titrations or UV spectrophotometric methods, which are tedious and time consuming.In the present paper, we report two extractive spectrophotometric methods based on the formation of ionassociation complexes between the antiallergic drugs and Bromopyrogallol Red (BPR) or Bromothymol Blue (BTB), which are more sensitive (ε = 1.03 -2.55 × 10 4 l mol -1 cm -1 ) than the official 10-12 (ε = 1.0 -2.1 × 10 3 l mol -1 cm -1) and the reported extractive 6 (ε = 5.43 × 10 3 l mol -1 cm -1 ) or direct 1-5 spectrophotometric methods (ε = 3.1 -9.61 × 10 3 l mol -1 cm -1 ) for the assay of the selected drugs, the structures of which are shown in Fig. 1. The proposed methods have been extended to the assay of these drugs in various pharmaceutical formulations. Experimental ApparatusAbsorbance measurements were made on a Hitachi UVvisible spectrophotometer U-2001 with 1 cm matched quartz cells. The pH measurements were made with a Schott Gerate pH meter CG 804. Elemental analysis was performed on a Thermoquest elemental analyzer EA 1110 CHN and a Nicolet FTIR spectrophotometer Impact 410 was used for recording the IR spectra of the complex. Reagents and samplesAll chemicals were of analytical or pharmaceutical grade and quartz-processed high-purity water was used throughout.Standard solutions of antiallergic drugs were prepared separately by dissolving 100 mg each of pure sample in distilled water and diluted up to the mark in a 100 ml volumetric flask. These solutions were stored in well-closed vessels, and direct contact with light was avoided. Standard solution was diluted as and when required. A 0.04% (w/v) of BPR and 0.05% (w/v) of BTB were prepared by dissolving first in a few drops of acetone and then diluted to the mark with distilled water in 100 ml calibrated flasks separately. Different buffers of various pH were prepared by following the standard methods. Determination of pure drugs Method using BPR.Aliquots of standard MDH or PMH solution were transferred into a series of 125 ml separating funnels. A 4 or 6 ml of BPR for MDH or PMH, 10 ml of chloroform and 5 ml of distilled water were added and mixed well....

Two simple, sensitive, and accurate spectrophotometric methods are proposed for the determination of levodopa (LD), methyldopa (MD), dopamine hydrochloride (DP), and pyrocatechol (PC) in pure and pharmaceutical preparations. The methods are based on measurement of the absorbances of tris( o-phenanthroline)iron(II) (method A) and tris(bipyridyl)iron(II) (method B) obtained by the oxidation of the catecholamines by iron(III) in the presence of 1,10-phenanthroline and 2,2′-bipyridyl at 510 and 522 nm, respectively. The absorbances were found to increase linearly with increases in the concentrations of the catecholamines, results which were corroborated by the calculated correlation coefficients (0.9990–0.9996). Beer's law was valid over the concentration ranges of 0.04–0.6, 0.06–0.75, 0.06–0.65, and 0.05–0.70 μg/mL in method A and 0.02–1.0, 0.04–1.3, 0.05–1.0, and 0.06–1.1 μg/mL in method B for PC, MD, LD, and DP, respectively. The common excipients and additives did not interfere in their determinations. The proposed methods were successfully applied to the assay of LD, MD, and DP in various dosage forms. The results were validated by statistical analysis.

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